Electronically controlled spectroscopic high voltage spark source



Feb. 8, 1966 A. BARDOCZ 3,234,431

ELEGTRONICALLY CONTROLLED SPECTROSCOPIC HIGH VOLTAGE SPARK SOURCE FiledJune 28.' 1961 R1 L R2 5 C3 4F INVENTOI; AJZPAD BARZDQCZ BY M AttorneysUnited States Patent 3 234,431 ELECTRONKIALLY CQNTROLLED SPECTRG- SCOPICHIGH VULTAGE SPARK SOURCE Arpad Bardcz, 4 Orlay Utca, Budapest XI,Hungary Filed June 28, 1961, Ser. No. 146,024 2 Claims. (Cl. 315-432)This is a continuation-in-part of my copending application, Serial No.688,694, filed Oct. 7, 1957, now abandoned.

In spectroscopic research work and spectrochemical analysis theself-ignited high voltage spark is frequently employed as light source.By self-ignited spark there is understood an electric discharge of acondenser charged to a relatively high voltage capable of breaking downa gap between two electrodes spaced several millimeters apart. 7 1 Theproduction of sparks is carried out, in the case of spectroscopic lightsources, in such a manner that condensers (working condensers) arecharged from the A.C. mains and the then discharged through theanalytical spark gap (eventually also through a controlling spark gap orspark gaps or electron tube connected in series with the analyticalspark gap). To obtain correct operation of the spark source, thecharging and discharging processes of the working condenser should beseparated from one another. This is necessary because if, during thespark discharge and immediately after it, the supply voltage remains onthe analytical and controlling spark gaps, in case of higher excitationenergies and greater spark frequencies the deionization of the sparkgaps is incomplete, consequently the networkwill be short circuitedthrough them and a regular controlling of the spark discharges cannot bemaintained. In other words, the spark source has to be formed in such amanner that, during charging of the condenser, no spark discharge shalltake place, while dur-- ing thedischarge the condenser shall becompletely separated from the charging network.

Recently, a further requirement consists in that in spark sources thestarting of spark discharges shall take place with a'smalltimescattering (jitter) of the order to magnitude of a microsecondrelative to the moment of a given control signal, so that spark sourcesmay be applied for the production of time resolved spark spectra. Thiscan be realized by means of electronically controlled spark sourcesoperating with high precision in time. In connection with the problemthe following should yet be noted.

In order to perform'spectroscopic analysis or investigations, andprimarily spectrochemical analysis, a single s'park'discharge is notsufficient to producea satisfactory spectrum on a photographic plate. Toproduce a satisfactory spectrum, many hundreds or even many thousands ofsuccessive discharges are necessary. These successive discharges must beresolved in time. That is, the particular time, during a each discharge,in which a is, the particular time, during each discharge, in which agiven spectrum occurs must be the same for each successive discharge.Thus, if it is, desired to use that portion of the discharge occurringbetween 0.0 and 0.1 microsecond of a given spark discharge, thesuccessive discharges m-ust also be analyzed within the 0.0 to 0.1microsecond range of the discharge. Thereby, the successive dischargesbeing analyzed will always be coincident in time with respect to theportion of the period of a single dicharge during which they occur.

The procedure by which corresponding time periods of successivedischarges appear at the same position on the photographic plate isknown as time resolution. One manner in which this time resolution maybe eflFected is by using a rotating mirror to direct the image of theare or spark discharge to the admission slit of the spectroice graph.With such an arrangement, each respective position along the slit willbe illuminated with light originating from the same respective timeperiods during the radiation of each successive discharge.correspondingly, every particular position on the spectrum line of aspectrum plate will be indicative of detection of the radiation arisingfrom the same particular period during the discharge of each successivespark or arc. It is thus imperative that a high time resolution must beeffected so that corresponding time portions of successive dischargeswill always appear at the same position on the spectrum line asphotographed on a spectrum plate. In other words, to obtain a high timeresolution, the superposition of the spectrum from successive dischargesmust be effected with a very high precision timewise. If this is done,corresponding increments of successive sparks or are discharges willappear exactly on the same place on the slit of the spectrograph, andevery successive corresponding spectrum will appear exactly on the sameplace on the photographic plate. It will therefore be apparent that ahigh time resolution is necessary when using a multitude of successivespark or are discharges to produce a photographic spectrum on thephotographic plate of a spectrometer.

The above mentioned requirement, manely that the charging anddischarging processes be separated from one another, can be relativelyeasily met if a number of sparks per second equal to the frequency ofthe network has to be produced. In this case, by inserting a rectifierbefore the working condenser, the charging of the condenser takes placeduring one of the half cycles of the A.C. network whereas the dischargetakes place during the other half cycle when the charged condenser iscompletely isolated from the mains by the rectifier. Hitherto theseparation of charging and discharging processes was solved in thismanner in the case of some spark sources.

In practical and scientific spectroscopic practice, however, in generala higher sparking frequency than the frequency of the network isdesirable. A higher spark frequency results in shorter exposition timesand in a higher analytical precision. Moreover, it is experimentallyproved that the higher the sparking frequency, the higher is thestability of the discharge, and consequently, the smaller is the timescattering at the production of time resolved spectra. It should benoted further that the time resolved spectroscopy for routine operationmay only be, in general, possible using a spark frequency higher thanthe mains frequency. In the majority'of cases, it is already sufficientif the frequency of the spark discharges is twice the frequency of theA.C. mains. i

The subject of the invention is a self-ignited spark source operatingwith high precision in time, also suitable for the production oftime-resolved spectra, with the aid of which the realization of asparking repetition rate per second higher than the mains frequency isfeasible in such I a manner that the charging and discharging processesof the condenser supplying the excitation energy are completelyseparated from one another. The charging and discharging processes ofthe working condenser are separated from each other in such a mannerthat said con; denser is charged with voltage pulses of a duration whichis very short as compared with the duration of the half period of themains supply voltage. Between the voltage pulses there is a voltage freeinterval. The voltage pulses of short duration are produced in anoscillatory circuit.

The appended drawing diagrammatically illustrates an embodiment of, andbest way for, carrying out the invention, which however, is not limitedto such embodiment. In the drawing the figure illustrates the circuitdiagram of an electronically controlled high precision spectrographiclight source.

F is the analytical spark gap and C2 is the Working condenser supplyingthe excitation energy. C2 discharges through auxiliary control gap S andair-cored transformer T. The excitation energy is induced in the circuitTC3-F. The role of condenser C3 will be explained later. C1 is a storagecondenser, V is a controllable electron tube which is controlled 'by thepulse generator IG by control voltage signals of very short duration.The frequency of the control voltage signals delivered by pulsegenerator 16 is variable. The working condenser C2 receives its chargefrom the storage condenser C1 through self-induction L, ohmic resistanceR2, and tube V. Condenser C1 is charged through high voltage transformerT, rectifier G, and if, when condenser C1 is charged, a positive voltagesignal is applied to the grid of tube V, which is ordinarily blocked bya negative bias, through the medium of a pulse generator G1, tube V willbecome conductive and charging of condenser C2 will commence. The taskof the ohmic resistance R2 and of self-induction L is to diminish thecurrent in the C1-L RZ-CZV circuit to the permissible loading of tube V.Condenser C2 is charged to a voltage which corresponds to the break-downvoltage of controlling spark gap S. As soon as the charging voltage ofC2 has reached the breakdown voltage of S, the latter breaks down and C2discharges through the path S-T.

Care must be taken that after the breakdown of S the supply voltageshould be disconnected from this gap. This takes place in the followingway: Owingto the design of the system, during the breakdown 'of S,condenser C1 has still a considerable charge, which begins to dischargein the form of an oscillation through the path LR2S-T-V. Besides thecurrent limiting role of L, its secondary role is further to ensure thedevelopment of oscillations in this circuit. However, this dischargewill have a duration of a quarter cycle of the frequency determined bythe data of the above mentioned circuit, since as soon as the directionof the current flow changes gas filled tube V .extinguishes and thecharging network is isolated :from the controlling spark gap S. Theinsertion of TandC3 isnecessary to divert the discharging current ofcondenser -C1 from the analytical spark gap F.

' It is mentioned here that the natural frequency of the circuitC1L.R2-ST-V is so low, as compared with the natural frequency of circuitC2S-T, that by the former induces practically no energy in the circuitT-C3-F.

In case of a single phase full wave rectification the number ofsparksproduced per second is twice the frequency ofthe mains, in case of athree phase half Wave rectification it isithreefold the frequency of thenetwork, in case of a three phasefull wave rectification it is sixfoldthe frequency of the network. If a large storage condenser is placedbetween R1 and the rectifier an unlimited number of sparks per .secondmight be attained.

It is understood from what has been set forth above that this inventionis not limited to the arrangements, devices, operations, conditions, andother details-specifically described above and illustrated, and can becarried out with various modifications without departing from the scopeofthe invention as defined in' the appended claims.

What I claim is:

1. A "high voltage spectroscopic spark and are source comprising, incombination, a device having an inputfor connection to asource of lowfrequency A.C. potential and producing relatively sharp output voltagepulses responsive to each half cycle of input potential and having aduration which is short in comparison with the duration of the halfcycle of said potential source; rectifying means connected to the outputof said device and adapted to produce rectified pulses corresponding tosaid output pulses; a charging circuit connected to the output of saidrectifying means and including a high voltage energy storing means; adischarge circuit including a discharge condenser across said chargingcircuit; said discharge circuit further including a controllableelectron tube which is normally current blocking and which istriggerable intoconductivity and which then remains conductive when thecurrent therethrough is above a specified value; means for triggeringsaid controllable electron tube operable at the conclusion of thechargingpulse-on said energy storage means to trigger said controllableelectron tube for current flow therethrough; and a further circuitacross said discharge condenser, said further circuit including acontrolling spark gap, an analytical spark gap, and circuit meanswhereby the discharge of said discharge condenser is effective first tobreak down said controlling spark gap and then to break down saidanalytical spark gap, said circuit means isolating said analytical sparkgap from said charging circuit.

2. A high voltage spectroscopic spark and are source comprising, incombination, a device having an input for connection to a source of lowfrequency A.C. potential and producing relatively sharp output voltagepulses responsive to each half cycle of input potential and having aduration which is short in comparison with the duration of the halfcycle of said potential source; rectifying means connected to theoutputof said device and adapted to produce rectified pulses corresponding tosaid output pulses; a charging circuit connected to the output of saidrectifying means and including a -high voltage energy storing means; adischarge circuit including a discharge condenser across said chargingcircuit; said discharge circuit further including a controllableelectron tube which is normally current blocking and which istriggerable into conductivity .andwhich then remains conductive when thecurrent therethrough is above a specified value; means for triggeringsaid controllable electron tube operable at the conclusion of thecharging pulse on said energy storage means to'triggersaid controllableelectron tube for current flow 'therethrough; and a further circuitacross said discharge condenser, said further circuit including acontrolling spark gap and an air-cored self-inductance across saiddischarge condenser, an analytical spark gap and a further condenserbeing connected across said inductance, the discharge of said dischargecondenser effective first to break down said controlling spark gap andthen to break down said analytical spark gap, said further condenser andinductance isolating said analytical spark gap from said chargingcircuit.

References Cited by the Examiner UNITED STATES PATENTS 3/ 1947 Hasler etal 315-237 7/1957 Lautenberger 315-209

1. A HIGH VOLTAGE SPECTROSCOPIC SPARK AND ARC SOURCE COMPRISING, INCOMBINATION, A DEVICE HAVING AN INPUT FOR CONNECTING TO A SOURCE OF LOWFREQUENCY A.C. POTENTIAL AND PRODUCING RELATIVELY SHARP OUTPUT VOLTAGEPULSES RESPONSIVE TO EACH HALF CYCLE OF INPUT POTENTIAL AND HAVING ADURATION WHICH IS SHORT IN COMPARISON WITH THE DURATION OF THE HALFCYCLE OF SAID POTENTIAL SOURCE; RECTIFIYING MEANS CONNECTED TO THEOUTPUT OF SAID DEVICE AND ADAPTED TO PRODUCE RECTIFIED PULSESCORRESPONDING TO SAID OUTPUT PULSES; A CHARGING CIRCUIT CONNECTED TO THEOUTPUT OF SAID RECTIFYING MEANS AND INCLUDING A HIGH VOLTAGE ENERGYSTORING MEANS; A DISCHARGE CIRCUIT INCLUDING A DISCHARGE CONDENSERACROSS SAID CHARGING CIRCUIT; SAID DISCHARGE CIRCUIT FURTHER INCLUDING ACONTROLLABLE ELECTRON TUBE WHICH IS NORMALLY CURRENT BLOCKING AND WHICHIS TRIGGERABLE INTO CONDUCTIVITY AND WHICH THEN REMAINS CONDUCTIVE WHENTHE CURRENT THERETHROUGH IS ABOVE A SPECIFIED VALUE; MEANS FORTRIGGERING SAID CONTROLLABLE ELECTRON TUBE OPERABLE AT THE CONCLUSION OFTHE CHARGING PULSE ON SAID ENERGY STORAGE MEANS TO TRIGGER SAIDCONTROLLABLE ELECTRON TUBE FOR CURRENT FLOW THERETHROUGH; AND A FURTHERCIRCUIT ACROSS SAID DISCHARGE CONDENSER, SAID FURTHER CIRCUIT INCLUDINGA CONTROLLING SPARK GAP, AN ANALYTICAL SPARK GAP, AND CIRCUIT MEANSWHEREBY THE DISCHARGE OF SAID DISCHARGE CONDENSER IS EFFECTIVE FIRST TOBREAK DOWN SAID CONTROLLING SPARK GAP AND THEM TO BREAK DOWN SAIDANALYTICAL SPARK GAP, SAID CIRCUIT MEANS ISOLATING SAID ANALYTICAL SPARKGAP FROM SAID CHARGING CIRCUIT.